WCDDL if you're experienced in PHP/HTML
DDLCMS if you are new to it, but I'd stay away from it


If you look at the current top DDL's:
Katz, Twilight, Mecho -> based on KDDL
Nexus, DDL0, Atomic, DownloadWarez, UnderNation -> based on WCDDL

There are no good DDL sites which are based on DDLCMS.